If an email message is sent to one of those email accounts (e.g. root@example1.com), it gets forwarded to the email address that is set under the Plesk Administrator's Profile.

How can this behavior be changed?

Answer

In the following output, it can be seen that all email sent to the accounts mentioned (for example root@localhost.localdomain) are forwarded to Plesk Administrator email address (for example pleskadmin@example.com):

Modify /etc/aliases file to forward all messages from desired accounts to another mailbox (for example john.doe@example.com).

For instance, for the account root@localhost.localdomain, add the following line into the /etc/aliases file:

CONFIG_TEXT: root: john.doe@example.com

Run the following command:

# postalias /etc/aliases

Verify that the setting applied:

# postmap -s /etc/aliases | grep root

This will not affect accounts created in Plesk with the name root@domainname.com, but if the mailbox does not exist then the message will be forwarded to john.doe@example.com instead of the Plesk Administrator email address.